Flora of New Zealand Series

≡Lichen petraeus Wulfen, Schr. Ges. naturf. Fr. Berlin 8: 89 (1787).

=Lecidea petraea var. neozelandica C.Knight, Trans. N.Z. Inst. 8: 318 (1876). Trans. Linn. Soc. ser. 2, Bot. 1: 277 (1877).

Lecidea petraea var. neozelandica. Type: New Zealand. Sine loco [probably Wellington], Charles Knight – WELT.

Description : Thallus whitish or grey-white, areolate, in spreading patches, 2–6 cm diam., without a marginal prothallus. Areolae 0.5–1.2 mm diam., plane, farinose, rarely smooth. Apothecia scattered or in small groups or concentric lines, sunk in thallus, rounded, 0.5–0.9 mm diam., disc black, matt, proper margin thin, white-pruinose. Epithecium grey-green or grey-brown to dark-brown or greenish black. Hymenium colourless, 100–140 μm tall. Hypothecium brown, red-brown or brown-black. Asci clavate, 8-spored, 80–110 × 20–40 μm. Ascospores colourless, muriform, 20–50 × 13–24 μm.

Chemistry : Thallus K+ yellow or K−, C−, KC−, Pd+ orange; containing stictic acid

N: (Wellington). S: Marlborough (Kaikoura). C: On calcareous substrata. Known also from Great Britain, Europe, Scandinavia, Greece, the Ukraine, North America and Tasmania (Feuerer 1978, 1991; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Wirth 1995a, 1995b; Kondratyuk et al. 1996a; Diederich & Sérusiaux 2000; Scholz 2000; Hafellner & Türk 2001; Llimona & Hladun 2001; Coppins 2002b; McCarthy 2003c, 2006; Nimis & Martellos 2003; Ihlen 2004a; Santesson et al. 2004).

Cosmopolitan

Illustrations : Knight (1876: pl. X, fig. 10 – as Lecidea petraea var. neozelandica; fig. 11 – as Lecidea petraea var.violacea; 1877: pl. XXXVII, fig. 13 – as Lecidea petraea var. neozelandica; fig. 14 – as Lecidea petraea var. violacea); Feuerer (1978: 93, 94); Wirth (1995a: 535, pl. 55O; 1995b: 805); Ihlen (2004a: 540, fig. 8D); Dobson (2005: 389).

Rhizocarpon petraeum is characterised by: the saxicolous (basicolous rocks) habit; a white, areolate, farinose thallus; innate apothecia with pruinose margins, often arranged in concentric lines; 8-spored asci; and colourless, muriform ascospores, 20–50 × 13–24 μm; and stictic acid in the medulla.